Self-assembled molecular architectures on surfaces: New strategies involving metal-organic copolymers

A combination of oligomeric porphyrin copolymers and bidentate Lewis bases has been used to construct 2-dimensional multilayer molecular architectures on siloxane-derivatized glass substrates. The key to this supramolecular chemistry is coordinate covalent bonding between zinc metalated porphyrins and bipyridyl "spacer" ligands, generating layers in an alternating, iterative fashion. UV-vis, XPS, AFM, and X-ray diffraction data support the formation of ordered thin film arrays. The stepwise deposition of each porphyrin layer is tracked by the linear increase in the absorbance of the porphyrin Soret band. XPS results demonstrate that the pyridinium coupling in the first monolayer is susceptible to X-ray decomposition during prolonged exposure. Extremely weak emission in the 600-800 nm region is attributed to the low chromophore concentration in the multilayer films. These results contrast sharply with those of spin-coated polymer thin films and represent an encouraging first step toward the design of new multilayer architectures.